The ability to harness the binding properties of monoclonal antibodies to catalyze chemical reactions has been demonstrated. The most generalized approach to elicit catalytic antibodies has been to synthesize haptenic molecules to mimic the proposed transition-state of the reaction of interest. Virtually all of the reactions performed so far are either concerted reactions, (Claisen, Diels-Alder) or involve the intermediacy of a tetrahedral transition-state, (ester-amide hydrolysis, transacylation). We propose to expand the repertoire of reactions catalyzed by antibodies to include those which proceed through transition states containing more than four ligands. Specifically, we will employ the transition-state stabilization method and synthesize haptens that mimic the pentacoordinate transition state proposed for phosphodiester hydrolysis. The haptens will be designed to possess the overall geometry of the pentacoordinate transition state, the presumed rate determining step found in the cleavage of internucleotide phosphodiester linkages. Based on a "bait and switch" tact, we have designed a set of haptens in a second effort to procure antibodies capable of hydrolyzing phosphodiester bonds. The underlining theme of this type of approach is the strategic placement of point charge(s) on the haptenic molecule. These charges can elicit complementary charged amino acid(s) in the antibody binding pocket that can function as acid/base catalysts to effect a chemical transformation of interest. Catalytic antibodies may be obtained by such clever hapten design. Also presumed, is that more efficient antibody catalysts may be conceived through second generation immunogens. Another approach, to compensate for possible deficiencies in the original hapten design, would be a molecular biological one. To increase the catalytic efficiency of antibodies obtained via our "bait and switch" methodology, a two-pronged approach ius proposed. First, the mapping of the antibody combining site will be accomplished by site- directed affinity labeling probes. Knowledge garnered here will be applied to the introduction of potential catalytic residues via site- directed mutagenesis. Besides increasing catalytic activity, we hope this multifaceted approach will provide a more complete understanding of an antibody's reaction mechanism. Ultimately, we hope to combine the catalytic properties of our monoclonal antibodies with their inherent binding specificities, to generate a class of proteins which can cleave phosphodiester bonds in a sequence specific manner.